This invention relates to digital communications, and more particularly to systems and methods for jointly demodulating a received signal in the presence of noise and interference.
Joint demodulation is widely used to detect a desired signal from a received signal that includes an interfering signal as well. In joint demodulation, the desired signal and the interfering signal are both demodulated based on information concerning the desired signal and the interfering signal, so as to obtain a better estimate of the desired signal.
Joint demodulation is described, for example, in U.S. Pat. No. 5,506,861 to Bottomley entitled System and Method for Joint Demodulation of CDMA Signals; U.S. Pat. No. 5,640,432 to Wales entitled Co-Channel Interference Suppression System; and U.S. patent application Ser. No. 09/143,821 to Hafeez et al., entitled Methods and Systems for Reducing Co-Channel Interference Using Multiple Timings for a Received Signal filed on Aug. 31, 1998 (now U.S. Pat. No. 6,304,618 to Hafeez et al.), and assigned to the assignee of the present invention. Joint demodulation also is described in the following publications: Hafeez et al., entitled Co-Channel Interference Cancellation for D-AMPS Handsets, Proceedings of the 49th IEEE Vehicular Technology Conference, May 1999, pp. 1026-1031; Murata et al., entitled Joint Frequency Offset and Delay Profile Estimation Technique for Nonlinear Co-channel Interference Canceller, Proceedings of the PIMRC, November 1998, pp. 486-490; and Lo et al., entitled Adaptive Equalization and Interference Cancellation for Wireless Communication Systems, IEEE Transactions on Communications, Vol. 47, No. 4, April 1999, pp. 538-545. The disclosures of all of the above-cited patents, patent application and publications are hereby incorporated herein by reference in their entirety.
Although joint demodulation can be highly effective in detecting a desired signal from a received signal that includes an interfering signal, joint demodulation may be more complex than standard or conventional demodulation, referred to herein simply as “demodulation”, of a received signal. Accordingly, there continues to be a need to provide improved systems and methods for jointly demodulating a received signal in the presence of an interfering signal.